Reference Electrode Types for Zero‐Gap CO2 Electrolyzers: Benefits and Limitations

Integrated reference electrodes allow to deconvolute voltage contributions of anode and cathode and contribute to a better understanding of CO2 electrolyzers. However, in zero‐gap cell configurations, this integration can be challenging and obtaining error‐free data with such a setup is a non‐trivial task. This study compares five different methods to integrate a reference electrode into an alkaline zero‐gap CO2 electrolysis cell. Sources of error and measures to circumvent them are investigated and finite‐element simulation is used to gain a better understanding of observed effects. Placing a reference electrode into the inactive area of the cell is found to be a reliable method, as long as the placement of electrodes is sufficiently controlled. Sandwiching a wire quasi‐reference electrode between two membranes is especially useful for electrochemical impedance spectroscopy; however, it can affect the overall cell performance. Contacting the catalyst layer from the backside with a salt‐bridge is promising for localized measurements if sufficient reproducibility can be ensured. Integrated reference electrodes can offer valuable insights into processes during zero‐gap CO2 electrolysis, required for further improvement. Different methods of integration, however, present unique benefits and limitations. This work compares five different methods based on experimental results and numerical simulation, highlighting practical challenges, and providing a guide for choosing a suitable setup.